Unreachable apparatus

The device did not respond to an INVITE or REGISTER

Both the terminals and the telephone gateways can be contacted for the normal functioning of the system, by sending SIP, INVITE and / or REGISTER requests. If the device does not respond to a first request, subsequent requests are sent, because the single packet could be lost (both the request and the response). Once a repetition limit value has been reached, the device is considered unreachable.

Possible causes:

  1. If the device to contact is a terminal or a gateway placed behind a NAT, we could find ourselves in the scenarios illustrated in case 1), the one relating to the connection timeout, a case to which we refer.
  2. In addition to the above, we may find ourselves in the presence of a NAT / Firewall configured to generate NAT UDP sessions with a timeout shorter than the duration of the SIP registration sessions. For example, with a 5-second timeout UDP NAT, all terminals / gateways would register without problems, but the nat would remain “punctured” only for 5 seconds every 60 or 120, making it impossible to contact the terminal / gateway in most of cases.
  3. If the gateway is that of a telephone operator on Public IP (not behind NAT), there may also be problems on the operator’s server.

Possible solutions:

  1. See the solutions of case 1) above, related to the connection timeout
  2. Check that the duration of the NAT sessions for the UDP protocol is at least 60 or 120 seconds, depending on what is set on the terminals / gateways
  3. Contact the support of the telephone operator for the appropriate checks